Process for producing protein concentrate or isolate and cellulosic thermochemical feedstock from brewes spent grains

ABSTRACT

A process for treating brewers spent grains for producing a high value protein product and a cellulosic residue, both from brewers spent grains that have not gone through fermentation. The high value protein product is useful as a protein supplement for human consumption, or feed for livestock and poultry. The cellulosic residue has value as a feedstock for a thermochemical process unit, such as for the production of a biofuel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application based on provisionalapplication 62/447,383 filed Jan. 17, 2017.

BACKGROUND OF THE INVENTION

This invention relates to a process for treating brewers spent grains,that have not gone through fermentation, for producing a high valueprotein product and a cellulosic residue product. The high value proteinproduct is useful as a protein supplement for human consumption, or feedfor livestock and poultry. The cellulosic residue product has value as afeedstock for a thermochemical process, such as for the production of abiofuel.

BACKGROUND OF THE INVENTION

Brewers spent grains (BSG) is the major by-product left after theprocessing of steeped, germinated, dried cereal gains (malt) for theproduction of beer and other malt products. Though barley is the primarygrain used for brewing, beers can also be made from other grains such aswheat, rye, maize, rice, oats, sorghum and millet. In general, BSGrepresents about 85% of the total by-products generated. BSG cangenerally be defined as a lignocellulosic material containing interalia, water, cellulose, non-cellulosic polysaccharides, lignin, crudeproteins, and crude fats. BSG is available in large quantitiesthroughout the year, but its main application has been limited to animalfeeding. Since BSG still contain proteins, there is a significantinterest in the brewing industry to further process the BSG to obtainmore valued products, particularly for human consumption.

Also, a substantial amount of research and development is undertaken inan effort to reduce our dependency on petroleum-based energy and to moveus toward more sustainable and environmentally friendly energy sources,such as wind energy, solar energy, and biomass. The conversion ofbiomass into transportation and other fuels is of great interest forreducing reliance on fossil fuels. Various biomass conversiontechnologies employ thermochemical processes, such as pyrolysis andgasification, that have relatively high capital and operating costs. Inparticular, sourcing and preparing biomass feedstocks, such as wood andagricultural residues, such as corn stover and soybean hulls, forpyrolysis or gasification, typically result in marginal productioneconomics.

Conventional processes have met with varying degrees of commercialsuccess for obtaining higher value products from brewers spent grains,but there still exist a need for improving efficiency and economics ofsuch processes. One such desired product is a high protein contentproduct suitable for human consumption.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a process forproducing a protein product, and a cellulosic product suitable as afeedstock for thermochemical processing, from brewers spent grainshaving a starch and protein content, and which have not gone throughfermentation, which process comprises:

a) introducing into a hydrolysis tank, with constant stirring, a mixturecomprised of: i) brewers spent grains having a protein content and astarch content, and which has not gone through fermentation, and ii) anamount of water so that the ratio of water to grains is from about 8:1to 11:1;

b) adding glucoamylase to the mixture in an amount that will convert atleast about 90 wt. % of the starch to sugars;

c) heating said mixture to a temperature from about 30° to about 70° C.;

d) cycling said heated mixture to and from a particle size reductionstage wherein the average size of grain particles, in said mixture, isreduced to an average size less than 500μ;

e) maintaining the temperature of about 30° C. to about 70° C. for aneffective amount of time to allow at least 95 wt. % of the starch of thegrains to be converted to sugars;

f) adjusting the pH of the mixture to a level from about 7 to 10.5;

g) adding an alkaline protease enzyme to the mixture in an amount tosolubilize 80 wt % to 90 wt % of the protein present;

h) passing the enzyme-containing mixture through a screen having 5 to500μ openings thereby resulting in a permeate comprised of proteins ofthe grains, the alkaline protease enzyme, and solids having a particlesize less than 5 to 500μ, and a retentate comprised of solids having aparticle size greater than 5 to 500μ;

i) passing said permeate resulting from step h) above to anultrafiltration stage comprised of a membrane having pores of 20 kDa to40 kDA in size, resulting in a retentate comprised of proteins greaterthan 20 kDA to 40 kDA in size, the alkaline protease enzyme, and fibermaterial; and a liquid permeate comprised of proteins smaller than 20kDA in size;

j) recycling the retentate from said ultrafiltration stage to thehydrolysis tank until there are no more proteins to hydrolyze, whereinduring recycling the pH of 7 to 10.5 and the temperature of about 30° C.to 70° C. of the mixture are maintained;

k) conducting the resulting liquid permeate from said ultrafiltrationstage to a nanofiltration stage wherein the resulting retentate has asolids content of from about 10 wt. % to about 50 wt. %; and

l) conducting the retentate having a solids content of about 10 wt. % toabout 50 wt. % solids to an evaporation stage wherein at least afraction of any remaining water is driven off thereby resulting in aproduct comprised of at least about 60 wt % to about 90 wt. % protein.

In a preferred embodiment of the present invention the brewers spentgrain is barley grain.

In another embodiment of the present invention the mixture is conductedto solids separation stage prior to being conducted to theultrafiltration stage, which solids separation stage to remove solidsspecies of the mixture that could clog the ultrafiltration membrane.

In yet another embodiment of the present invention the permeate from theultrafiltration stage is conducted to a heat treatment stage wherein itis subjected to temperatures capable of deactivating any remainingenzymes in the mixture.

In still another embodiment of the present invention the solidsseparation stage is comprised of microfiltration membrane.

BRIEF DESCRIPTION OF THE FIGURE

The FIGURE hereof is a flow diagram illustrating one preferredembodiment of the present invention. Dashed line in this FIGURErepresent optional embodiments to the instant process.

DETAILED DESCRIPTION OF THE INVENTION

Any brewers spent grains can be used for the practice of the presentinvention as long as they have not been subjected to fermentation, asdistillers grains have. Non-limiting examples of such grains includebarley, wheat, rye, maize, rice, oats, sorghum and millet Preferred isbarley.

The present invention can be better understood with reference to theFIGURE hereof. The instant process is generally practiced by introducinginto hydrolysis tank HT brewers spent grains and an effective amount ofwater to achieve a ratio of water to grains, on a dry weight basis of8:1 to 11:1. It is preferred that the ratio of water to grains be fromabout 9:1 to 10:1. Brewers spent grains received from a brewer aretypically in a wet condition. The ratio of water to grains for wetgrains received directly from a brewer will typically be from about 3:1to about 6:1, more typically from about 3.5:1 to about 5:1. Thus, waterwill need to be added to achieve the desired ratio of water to grainsfor the process of this invention. Hydrolysis tank HT can be constructedfrom any suitable material, preferably a stainless steel. It can be openat the top, or enclosed with a suitable cover containing ports forallowing entry of water, grains, and any other ingredient, or reactant,needed for the practice of the present invention. Hydrolysis tank HTwill also contain a stirring apparatus (not shown) of suitable corrosionresistant material. It is preferred that the mixture contained inhydrolysis tank HT be constantly stirred throughout the instant process.

The pH of brewers grains typically received form a brewer will normallybe in the range of about 3.5 to about 6.5. If they are not in that pHrange, the pH can easily be adjusted, usually with use of a suitableacid. The preferred pH range is from about 4.5 to 5.5. The acid used canbe any suitable acid that is capable of achieving the desired pH range.The acid can be either an inorganic acid, preferably hydrochloric acid,or an organic acid, such as a carboxylic acid. The acidic mixture isthen heated to a temperature from about 30° C. to about 70° C.,preferably from about 40° C. to about 60° C. An effective amount ofglucoamylase is added to the mixture in an amount that will convert atleast about 90 wt. % of the starch to sugars About 0.1 wt. % to about0.2 wt. %, preferably about 0.15 wt. % of glucoamylase, on a dry weightbasis, is added. It will be understood that the terms “mixture” and“slurry” can be used interchangeably herein. It will also be understoodthat it is not critical to the instant process that the glucoamylase beadded after the mixture is heated. For example, the glucoamylase can beadded and then the mixture heated to 30° C. to 70° C.

The mixture is continually cycled to and from particle size reductionzone M1 via lines 10, 12, and 16. A particle size reduction stage canalso sometimes be referred to herein as a milling stage. Any suitableparticles size reduction equipment can be used that is capable ofreducing the size of particles in an aqueous mixture or slurry,preferably at a water to grains ratio of 8:1 to 11:1. It is preferredthat a colloid mill or rotor stator type of mill be used. More preferredis high-shear rotor-stator wet milling equipment. Rotor-stator wetmilling equipment is well known in the art and can be commerciallyobtained from such companies as Kady International having a facility inScarborough, Me.; Custom Milling & Consulting Inc having a facility inFleetwood, Pa.; and Chemineer having a facility in Dayton, Ohio. Theaqueous mixture is milled for an effective amount of time. That is, forthat amount of time that will result in an average particle size ofgrains in the mixture to be less than about 500 microns (μ). This amountof time will typically be from about 30 minutes to about 60 minutes,preferably for about 45 minutes. The temperature and pH are maintainedfor an effective amount of time in order to hydrolyze substantially allof the starch from the grains. By substantially all we mean at leastabout 90 wt. %, preferably greater than 95 wt. %, and more preferably atleast about 98 wt. % hydrolyzed. It is most preferred that substantiallyall of the starch be converted to sugars. That is, wherein only a verysmall percent, for example less than about 1 wt. %, more preferably lessthan about 0.5 wt. % is left unconverted. This amount of time willtypically be from about 20 minutes to about 60. The hydrolyzing processtakes about 30 to 45 minutes which allows time to effectively mill thegrain. The grains are most likely completely milled to the desired sizein about 20 minutes, but extra time is preferred to allow the starch inthe grains to be converted to sugar.

The pH of the resulting mixture in hydrolysis tank MV is brought toabout 7 to 10.5, preferably from about 8 to 10, more preferably to about8.5 to 9.5 with use of a suitable aqueous base solution. It is preferredthat an alkali or alkaline earth metal aqueous solution be used, morepreferred is the use of sodium hydroxide. The resulting treated mixtureis then passed through a screen SN having 60μ openings resulting in anaqueous permeate containing proteins and solids having an averageparticle size less than 60μ and a retentate comprised of solids having aparticle size greater than 60μ.

The permeate that passes through screen SN is then conducted via line18, along with an alkaline protease enzyme introduced into line 18 vialine 19, to ultrafiltration stage UF. The amount enzyme introduced intoline 18 will be an effective amount that will be at least that amount tosolubilize 80 wt % to 90 wt % of the protein present. Such an amountwill be from about 0.1 wt. % to about 0.3 wt. %, preferably about 0.25wt. %, on a dry weight basis. It is also preferred that the alkalineprotease enzyme be alcalase. Ultrafiltration stage UF will be comprisedof a suitable membrane having pores of a size of about 0.5 to 1.5 kDA.he term kDa is well known in the art and is used as a measure ofmolecular weight or mass. For example, one hydrogen atom has a mass of 1Da. Proteins and other macromolecule molecular weights are usuallymeasured in kDa or kilodaltons wherein 1 kDa is 1000 Da (daltons). Theresidence time of the mixture passing through the ultrafiltrationmembrane will be long enough to allow hydrolysis of both starch andlarger size proteins to take place. It will be understood thathydrolysis of proteins takes place in both hydrolysis tank HT andultrafiltration stage UF.

There may be an occasion to provide a coarser filtering step prior toultrafiltration stage UF. One occasion to use a course filter prior toultrafiltration is when the mixture is such that it begins to clog theultrafiltration membrane, thereby preventing a suitable flow-through andpreventing the ultrafiltration membrane from adequately performing itsintended function. If the mixture is to be filtered prior toultrafiltration stage UF, then the mixture flowing through line 18 isdiverted through line 100 to first separation stage S1. Any suitablesolids separation equipment can be used for S1 as long as it is capableof filtering out solids greater than about 100 kDA. Non-limitingexamples of such suitable equipment include a microfiltration membrane,a hydrocyclone, and a decanting centrifuge. Preferred is amicrofiltration membrane having pores of about 100 kDA in size. Thepermeate from this first separation stage will be sent, via line 110 toultrafiltration stage UF. The retentate from S1 will be recycled tohydrolysis tank HT via lines 120 and 16.

The permeate from ultrafiltration stage UF, which contains substantiallyall of the lower molecular weight proteins is preferably conducted tonanofiltration stage NF via line 20. It is within the scope of thisinvention that the permeate from ultrafiltration stage UF be heattreated prior to nanofiltration stage NF in the event there are stillalkaline protease enzymes remaining in the permeate. If heat treatmentis desired the permeate is passed via line 200 through heat treatmentstage H which is operated at an effective temperature to deactivate anyremaining enzymes. This temperature will be an effective temperature tocause deactivation of the enzyme. This temperature will typically befrom about 75° C. to 100° C., preferably from about 80° C. to 85° C. Themixture is then held at that temperature for an effective amount of timeto ensure that the enzyme is deactivated. This effective amount of timewill be from about 2.5 to about 30, preferably from about 5 to 20minutes, more preferably about 15 minutes. Any suitable heat treatmentequipment can be used. One heat treatment type of equipment preferredfor the practice of the present invention is pasteurization equipment.The heat treated permeate is then passed to nanofiltration stage NF vialines 210 and 20.

The retentate from ultrafiltration stage UF, which may still containhigh molecular weight proteins, fiber material and fats, is recycled vialine 21 and 16 to hydrolysis tank HT until there are no more proteins tohydrolyze. High molecular weight proteins, for purposes of thisinvention, those that stay in the retentate of the UF membrane, are >20kDA. The molecular weight of the proteins passing through the UFmembrane are less than 20 kDA. At the NF stage, proteins and any otherspecies that are <1 kDA, which include amino acids and very lowmolecular weight proteins are removed.

Nanofiltration is well known in the art and is a membranefiltration-based method that uses nanometer sized cylindricalthrough-pores that pass through the membrane at 90°. Nanofiltrationmembranes have pore sizes from 0.5 to 1.0 kDa, which is smaller thanthat used in microfiltration and ultrafiltration, but typically largerthan reverse osmosis. The retentate from the nanofiltration stage willtypically be comprised of about 20 to 50 wt. % solids and is passed vialine 22 to evaporation stage VE which is preferably performed under avacuum wherein the solids content of the stream is increased to about 50to 60 wt. % solids. The stream exiting evaporation stage VE is passedvia line 24 to first drying stage D1 to drive off at least a fraction ofthe water and to concentrate the protein. It is preferred thatsubstantially all of the water be driven off by the use of a spray drierto result in a powdered protein product. It is also within the scope ofthis invention that an ultrafiltration membrane be used that has poreslarge enough to allow the enzyme to pass through. Such a membrane wouldbe those whose pores are greater than about 20 kDA, particularly thosehaving pores in the range of about 30 to 100 kDA. In such a case, theuse heating treatment stage H is preferred.

The permeate from the nanofiltration stage NF can optionally be sent vialine 300 to a reverse osmosis unit RO so that clean, low solids watercan be recycled back to the hydrolysis tank HT via line 310 for waterconservation purposes. The clean water is the permeate from reverseosmosis unit RO. The retentate from reverse osmosis RO is preferablydisposed of as wastewater via line 320. The RO membrane will have poresfrom about 100 to 500 daltons, so everything larger than that will beremoved from the water stream.

The retentate of that does not pass through 60μ screen SN situated downthe bottom of hydrolysis tank HT remains in extraction tank andcontinues to be recycled to and from first particle size reduction stageM1. Of course, as grain particles become less than 60μ in size they willeventually pass through screen SN and be conducted to ultrafiltrationstage UF. Those particles greater than 60μ that are left in the uppersection of hydrolysis tank HT are conducted via line 26 as an aqueousslurry to second liquid/solids separation stage S2 wherein the solidsare separated, sent via line 28 to second dryer D2, then via line 30 tosecond milling stage M2 to result in a fiber flour product.

Alternative hydrolysis conditions can include: temperatures from about10° C. to about 100° C., preferably from about 20° C. to about 80° C.,more preferably from about 30° C. to about 70° C. and most preferablyfrom about 40° C. to about 60° C.; and times from about 30 minutes to180 minutes, preferably from about 60 minutes to about 150 minutes, andmore preferably from about 90 minutes to about 130 minutes.

In a preferred embodiment, the treated spent brains be subjected to aneffective amount of ultrasonic energy to improve the efficiency of theprotein extraction portion of the process. The preferred effectiveultrasonic energy input is from about 3 to about 30 Joules/gram ofgrains with a frequency of about 40 kHz with about 3 to about 10Joules/gram being preferred.

The following additional embodiments are also within the scope of thisinvention; i) the use of a debittering exo-peptidase prior to the dryingstep at a pH between 6.5-9 and a temperature of 45° C. to about 65° C.for 30 to 120 minutes to reduce protein bitterness; ii) the use adebittering exo-peptidase during the alcalase addition step to reduceprotein bitterness; iii) performing the milling step prior to theaddition of glucoamylase, iv) include the addition of alpha-amylaseand/or beta-amylase during the glucoamylase addition step to increasestarch hydrolysis of branched chains; v) separate the water and fromgrains immediately following the glucoamylase addition step whichremoves the glucose from the process prior to solubilizing the protein,then add additional water to the grains to bring the water to grainsratio back to 9:1 and continue the process as normal; vi) the use of amild milling to separate the husk from the rest of the grain, thenseparate from the grain and continue the process as normal after huskremoval; and vii) during the glucoamylase addition step, add aneffective amount of glucose oxidase, which will oxidize the glucose toform hydrogen peroxide which will lighten the color of the end productsand reduce the glucose content, then continue the process as normal.

Also within the scope of this invention is a brewery process wherein acereal grain is processed to produce a beer and leaving a substantialamount of spent grains as a by-product. The spent grains are thenprocessed in accordance with the process herein described for obtaininga concentrated protein product and a cellulosic product from the spentgrains. Conventional beer making steps typically require that a cerealgrain, preferably barley, be prepared for brewing by a process involvingmalting, heating, drying out, and cracking open the husks of the kernelsof the grains, which helps expose the starches during the mashingprocess. In mashing, the grains are steeped in hot, but not boilingwater for an effective amount of time, typically about an hour. Thisactivates enzymes in the grains that cause it to break down the starchinto sugars. Once this is done the water is drained from the mash, whichis now rich in sugar from the grains. A sticky, sweet liquid referred toas “wort” is produced and it is often referred to as unmade beer. Thewort consists primarily of sugars and water resulting from mashing. Atthis point lautering can be used to separate the wort from spent grainsas efficiently as possible. Once the wort has been separated from thegrains in the lautertun, the process described herein can be performedusing the lautertun as the extraction tank. The lautertun has a falsebottom with a screen that can act as the 60 micron screen previouslydescribed. It also contains a stirring mechanism.

The wort is boiled for an effective amount of time then hops and otherspices are added. Hops provide bitterness to balance out the sugar inthe wort and provide flavor. Once the wort is cooled, strained, andfiltered and put into a fermentation vessel wherein yeast is added. Atthis point the brewing is complete and fermentation begins. The beer isstored for a few weeks at cold temperatures in the case of lagers, whilethe yeast works its magic by eating up the sugar and producing carbondioxide and alcohol and waste products. The resulting beer can then beconditioned so it can mature and become smooth and by-products offermentation diminished. The beer can be subjected to secondaryfermentation.

What is claimed is:
 1. A process for producing a protein product, and acellulosic product suitable as a feedstock for thermochemicalprocessing, from brewers spent grains having a starch and proteincontent, and which have not gone through fermentation, which processcomprises: a) introducing into a hydrolysis tank, with constantstirring, a mixture comprised of: i) brewers spent grains having aprotein content and a starch content, and which has not gone throughfermentation, and ii) an amount of water so that the ratio of water tograins is from about 8:1 to 11:1; b) adding glucoamylase to the mixturein an amount that will convert at least about 90 wt. % of the starch tosugars; c) heating said mixture to a temperature from about 30° to about70° C.; d) cycling said heated mixture to and from a particle sizereduction stage wherein the average size of grain particles, in saidmixture, is reduced to an average size less than 500μ; e) maintainingthe temperature of about 30° C. to about 70° C. for an effective amountof time to allow at least 95 wt. % of the starch of the grains to beconverted to sugars; f) adjusting the pH of the mixture to a level fromabout 7 to 10.5; g) adding an alkaline protease enzyme to the mixture inan amount to solubilize 80 wt % to 90 wt % of the protein present; h)passing the enzyme-containing mixture through a screen having 5 to 500μopenings thereby resulting in a permeate comprised of proteins of thegrains, the alkaline protease enzyme, and solids having a particle sizeless than 5 to 500μ, and a retentate comprised of solids having aparticle size greater than 5 to 500μ; i) passing said permeate resultingfrom step h) above to an ultrafiltration stage comprised of a membranehaving pores of 20 kDa to 40 kDA in size, resulting in a retentatecomprised of proteins greater than 20 kDA to 40 kDA in size, thealkaline protease enzyme, and fiber material; and a liquid permeatecomprised of proteins smaller than 20 kDA in size; j) recycling theretentate from said ultrafiltration stage to the hydrolysis tank untilthere are no more proteins to hydrolyze, wherein during recycling the pHof 7 to 10.5 and the temperature of about 30° C. to 70° C. of themixture are maintained; k) conducting the resulting liquid permeate fromsaid ultrafiltration stage to a nanofiltration stage wherein theresulting retentate has a solids content of from about 10 wt. % to about50 wt. %; and l) conducting the retentate having a solids content ofabout 10 wt. % to about 50 wt. % solids to an evaporation stage whereinat least a fraction of any remaining water is driven off therebyresulting in a product comprised of at least about 60 wt % to about 90wt. % protein.
 2. The process of claim 1 wherein the brewers spentgrains are spent barley grains.
 3. The process of claim 1 wherein theratio of water to grains is about 9:1 to about 10:1.
 4. The process ofclaim 1 wherein the particle size reduction is performed with a rotorstator mill.
 5. The process of claim 1 wherein at least 95 wt. % of thestarch is converted to sugars in step e)
 6. The process of claim 7wherein at least 98 wt. % of the starch is converted to sugars.
 7. Theprocess of claim 1 wherein the alkaline protease enzyme is alcalase. 8.The process of claim 1 wherein the pH is adjusted during step a) toabout 3.5 to about 6.5.
 9. The process of claim 1 wherein pasteurizationis performed at a temperature from about 70° C. to about 90° C.
 10. Theprocess of claim 1 wherein the membrane used in the nanofiltration stagecontains pores in the range of 500 to 1000 daltons.
 11. The process ofclaim 1 wherein the enzyme-containing mixture from step h) herein isfirst passed through a separation stage capable of separating out solidsgreater than about 100 kDA in size prior to being passed to saidultrafiltration stage.
 12. The process of claim 11 wherein theseparation stage is microfiltration stage containing a microfiltrationmembrane having pores of about 100 kDA in size.
 13. The process of claim1 wherein the permeate from said ultrafiltration stage is passed to aheat treatment stage wherein it is subjected to an effective temperatureof deactivating any enzymes present in the permeate.
 14. The process ofclaim 1 wherein the permeate from said nanofiltration stage is conductedto a reverse osmosis stage wherein particles greater than about 200daltons will be removed.